Data communications systems or networks generally comprise channels for sending and receiving data. A number of wired communications systems or networks, such as cable, Ethernet and Gigabit Ethernet systems, generally include stationary channels. A stationary channel is generally one in which the channel response and the noise statistics do not vary significantly or regularly (if at all) over time. Techniques are available for such systems and networks to reduce the adverse effects of fluctuations in communications parameters. However, such techniques generally do not affect communications parameters that tend to fluctuate over time.
Certain communications systems or networks, such as powerline systems or networks, include cyclostationary channels. A cyclostationary channel is one in which the channel response, the noise statistics and/or channel attenuation vary periodically. Also, powerline channels, which use conventional AC power lines for communications, experience regular fluctuations in noise and signal attenuation. The period of the noise power function in a powerline channel is generally the inverse of its frequency. In a typical case, that period is ( 1/120 Hz), or 8.3 msec. Noise in a powerline channel may also be introduced by other sources (such as a zero sequence current), some of which may be periodic (e.g., harmonics such as a third harmonic). During “spikes” in the noise power in a powerline channel, the signal-to-noise ratio (SNR) can be reduced sufficiently to cause errors in the data. Particularly when the signal strength is low, a low SNR can cause significant reliability problems.
A need therefore exists to increase the reliability of data communicated in channel in which time-dependant fluctuations are a potential source of error, to reduce errors and/or shutdowns in networks that include such cyclostationary channels.